On 3H β-Particle and 60Co γ Irradiation of Aqueous Systems

Abstract Harris, R. E. and Pimblott, S. M. On 3H β-Particle and 60Co γ Irradiation of Aqueous Systems. Radiat. Res. 158, 493–504 (2002). The chemistry of water and aqueous solutions is very different after irradiation with 3H β particles and high-energy electrons or 60Co γ rays. The greater the linear energy transfer (LET) of the medium for 3H β particles compared to high-energy electrons or 60Co γ rays leads to an increased local concentration of reactants. There is an increased amount of intratrack chemistry, which reduces the escape yield of eaq− and OH by about 50%, but increases the yield of H2 by about 50% and of H2O2 by about 35%. Analysis of stochastic-diffusion kinetic calculations employing simulated track structures reveals that the yield of H2 produced by diffusion-kinetic processes increases significantly for 3H β particles compared to 60Co γ radiation, while production of H2 by sub-picosecond processes is essentially the same. In both 3H β-particle and 60Co γ radiolysis, the reactions (eaq− + eaq−) and (eaq− + H) are equally important in the production of H2. In the former case, each reaction has a yield of ∼0.18, and in the latter a yield of ∼0.08. In neutral water, the reaction (H + H) is negligible. The yield of Fe(III) in 3H β-particle radiolysis of the Fricke dosimeter is much smaller than in radiolysis with more energetic electrons. Simulations show that this change is primarily due to the reduced escape yield of H, formed from the scavenging of eaq− by the bulk H3O+ of the acid. The chemical differences observed in experiments, and in calculations, reflect the underlying structure of the electron tracks: Examination of the track structure simulations demonstrates that primary events are considerably more well-separated in high-energy electron tracks compared to 3H β-particle tracks.